Rob Matson found a possible comet in SWAN-images taken between Nov. 7 and 19 November, moving from the constellation Telescopium into Sagittarius. Matson computed a parabolic orbit that he circulated via e-mail to solicit ground-based observations to seek confirmation of the possible comet. Terry Lovejoy obtained images through trees and in moonlight on Nov. 29.4 UT with a 20-cm reflector that showed a well-condensed comet of diameter 2' and mag about 10. On the following day R.H. McNaught took additional images of comet C/2012 V4 using the 0.5m Uppsala Telescope at Siding Spring. They showed an onion-like 1.0' coma with a very condensed central condensation and a 6' tail in p.a. 101°. On Dec. 1 Alan Hale could observe the comet visually, estimating a 2.2' coma of total magnitude 9.4.

Maik Meyer suggested that the comet's orbital elements are similar to those of comet P/Pons-Gambart (1827 II). However S. Nakano did not succeed to calculate an orbit with a period of about 62 years (assuming that the perihelion passages in 1889 and 1951 went unobserved) matching the observed positions of 1827 with satisfying precision. However, it is known that the observed positions of 1827 are extremely noisy. Additional astrometric observations then showed that the comet moves around the sun on an orbit with a period of 188 years, which represents all observed postions with sufficient precision, indicating that this is the next perihelion passage after discovery. However, the comet is 2 mag fainter than in 1827. Since the current orbital elements - except excentricity - are very similar to the ones derived from the 1827 passage and the orbital arcs of ellipses of periods 62 and 188 years are almost the same near the sun, the comet was found only 1/2° aside the path that was predictable with the old orbital elements. Comet C/2012 V4 (Pons-Gambart) passed perihelion on Dec. 19, 2012. In the meantime it received the permanent designation 273P/Pons-Gambart (CBET 3320/21, MPEC 2012-Y30 und -Y43)

Shortly after its recovery the comet disappeared in the twilight for four weeks. When it eventually reached comfortable altitudes it had faded considerably. Therefore only 5 observations by 2 members of the German Comet Section and 25 international observations could be used for the analysis. These indicate a brightness evolution according to the formula

which yield a maximum brightness of 8.8 mag in mid-December 2012. At the end of the first week in April the comet had faded to 13.0 mag.

Total Brightness and Coma Diameter

Shortly after recovery the coma measured 3' (200.000 km), decreasing continuously to 1.0' (70.000 km) until the beginning of April. At recovery the coma was well-condensed (DC 5), but grew ever more diffuse with every passing week, reaching DC 2 at the start of April. Visual tail sightings were very rare.

Andreas Kammerer

FGK observations